An air bag safety restraint in the form of an inflatable restraining curtain disposed along the side of a vehicle between an occupant and window or door openings plays a well recognized role in preventing injury to the occupant during a collision event. Typically, such air bags are inflated rapidly by the pressure of a reaction gas released from an inflator at the outset of the collision event. This gas generation typically takes place when a gas-generating agent in an inflator induces a chemical reaction activated by a collision signal from a collision detecting sensor. The gas which is generated by the inflator is then conveyed to the air bag. Inflatable restraint curtains are typically deployed downwardly from a storage position along the roof rail so as to at least partially cover window and/or door openings across the side of the vehicle. The deployed curtain thus provides both a degree of cushioning restraint as well as a barrier preventing the occupant from being ejected from the vehicle. Due to the extended duration of a roll-over collision event where the vehicle may turn over several times, it is desirable for the curtain-type air bags to remain in inflated tension for an extended period of time so as to maintain a degree of head protection and barrier restraint until the entire event is concluded. Preferably, such curtain-type restraint cushions remain inflated for about 6 seconds or more.
Air bag cushions formed by sewing together panels of fabric typically cannot maintain inflation for extended periods of time. Performance can be improved by applying substantial quantities of permeability blocking coating materials. However, applying sufficient coating weights to the fabric layers gives rise to substantial weight increase and bulk thereby increasing cost and making storage more difficult. Since the gas release in a sewn air bag is predominately at the seams, one solution that has been utilized is to weave the air bag as a one piece structure on a Jacquard loom and to then apply a relatively heavy layer of permeability blocking coating to cover the entire structure including the woven in seams. While Jacquard weaving has provided bag structures meeting desired performance requirements, the practice is nonetheless relatively expensive and inefficient to carry out. Moreover, even with woven in seams, air bags such as curtain type bags that are required to maintain inflation for extended periods may still require relatively high coating weights.
The ability to maintain tension-inducing pressure in sewn air bag curtains of large volume has been particularly problematic. Such curtains are used in vehicles of extended length such as sport utility vehicles, vans and the like.